diff --git a/index.php b/index.php
index b10d876..15fd0df 100644
--- a/index.php
+++ b/index.php
@@ -10,7 +10,7 @@
  *   the currently supported data collections/API endpoints in the README.md file
  * - this tool currently supports versions 4.x and 5.x of the UniFi Controller software
  *
- * VERSION: 1.0.7
+ * VERSION: 1.0.8
  *
  * ------------------------------------------------------------------------------------
  *
@@ -20,13 +20,24 @@
  * with this package in the file LICENSE.md
  *
  */
-define('API_BROWSER_VERSION', '1.0.7');
+define('API_BROWSER_VERSION', '1.0.8');
 
 /**
  * in order to use the PHP $_SESSION array for temporary storage of variables, session_start() is required
  */
 session_start();
 
+/**
+ * check whether user has requested to clear the PHP session
+ * - this function can be useful when login errors occur, mostly after upgrades or incorrect credential changes
+ */
+if (isset($_GET['reset_session']) && $_GET['reset_session'] == true) {
+    $_SESSION = array();
+    session_unset();
+    session_destroy();
+    session_start();
+}
+
 /**
  * starting timing of the session here
  */
@@ -707,6 +718,8 @@ function sites_sort($a, $b)
                         <li id="united"><a href="?theme=united">United</a></li>
                         <li id="yeti"><a href="?theme=yeti">Yeti</a></li>
                         <li role="separator" class="divider"></li>
+                        <li id="reset_session" data-toggle="tooltip" data-placement="top" data-original-title="In some cases this will fix login errors (empty sites list)"><a href="?reset_session=true"><i class="fa fa-refresh"></i> Reset PHP session</a></li>
+                        <li role="separator" class="divider"></li>
                         <li id="info" data-toggle="modal" data-target="#aboutModal"><a href="#"><i class="fa fa-info-circle"></i> About UniFi API Browser</a></li>
                     </ul>
                 </li>
@@ -833,11 +846,15 @@ function sites_sort($a, $b)
     /**
      * highlight and mark the selected options in the dropdown menus for $controller_id, $action, $site_id, $theme and $output_format
      * NOTE:
-     * these actions are performed conditionally when values are set for the respective PHP variables
+     * these actions are performed conditionally if values are set for the respective PHP variables
      */
     ('<?php echo $action ?>' != '') ? $('#<?php echo $action ?>').addClass('active').find('a').append(' <i class="fa fa-check"></i>') : false;
     ('<?php echo $site_id ?>' != '') ? $('#<?php echo $site_id ?>').addClass('active').find('a').append(' <i class="fa fa-check"></i>') : false;
     ('<?php echo $controller_id ?>' != '') ? $('#controller_<?php echo $controller_id ?>').addClass('active').find('a').append(' <i class="fa fa-check"></i>') : false;
+
+    /**
+     * these two options have default values so no conditions needed here
+     */
     $('#<?php echo $output_format ?>').addClass('active').find('a').append(' <i class="fa fa-check"></i>');
     $('#<?php echo $theme ?>').addClass('active').find('a').append(' <i class="fa fa-check"></i>');
 
diff --git a/phpapi/class.unifi.php b/phpapi/class.unifi.php
index 320da1d..4543316 100644
--- a/phpapi/class.unifi.php
+++ b/phpapi/class.unifi.php
@@ -9,7 +9,7 @@
  * and the API as published by Ubiquiti:
  *    https://www.ubnt.com/downloads/unifi/5.3.8/unifi_sh_api
  *
- * VERSION: 1.0.11
+ * VERSION: 1.0.12
  *
  * NOTES:
  * - this Class will only work with UniFi Controller versions 4.x and 5.x. There are no checks to prevent
@@ -26,7 +26,7 @@
  * with this package in the file LICENSE.md
  *
  */
-define('API_CLASS_VERSION', '1.0.11');
+define('API_CLASS_VERSION', '1.0.12');
 
 class unifiapi {
     public  $user         = '';
@@ -37,7 +37,6 @@ class unifiapi {
     public  $is_loggedin  = FALSE;
     public  $debug        = FALSE;
     private $cookies      = '';
-    private $payload_len  = '';
     private $request_type = 'POST';
 
     function __construct($user = '', $password = '', $baseurl = '', $site = '', $version = '') {
@@ -524,14 +523,15 @@ public function list_guests($within = 8760) {
     }
 
     /**
-     * List client devices
-     * -------------------
-     * returns an array of client device objects
+     * List online client device(s)
+     * ----------------------------
+     * returns an array of online client device objects, or in case of a single device request, returns a single client device object
+     * optional parameter <client_mac> = the MAC address of a single online client device for which the call must be made
      */
-    public function list_clients() {
+    public function list_clients($client_mac = NULL) {
         if (!$this->is_loggedin) return FALSE;
         $return          = array();
-        $content_decoded = json_decode($this->exec_curl($this->baseurl.'/api/s/'.$this->site.'/stat/sta'));
+        $content_decoded = json_decode($this->exec_curl($this->baseurl.'/api/s/'.$this->site.'/stat/sta/'.$client_mac));
         if (isset($content_decoded->meta->rc)) {
             if ($content_decoded->meta->rc == 'ok') {
                 if (is_array($content_decoded->data)) {
@@ -549,7 +549,7 @@ public function list_clients() {
      * Get data for a single client device
      * -----------------------------------
      * returns an object with the client device information
-     * required parameter <client_mac> = client MAC address
+     * required parameter <client_mac> = client device MAC address
      */
     public function stat_client($client_mac) {
         if (!$this->is_loggedin) return FALSE;